Consumer photographs are often taken with inexpensive cameras and under less than ideal conditions. These shortcomings tend to result in a large percentage of printed images that are less than acceptable. Silver halide and thermal transfer printing systems are marketed by the Eastman Kodak Company of Rochester, N.Y., that include automatic image enhancement of photographic prints, known as Kodak Perfect Touch™, which includes noise reduction.
Noise characteristics are different in different types of printing systems. In electrostatographic systems, some of the noise characteristics relate to the use of toner, which is particulate that is fused to produce an image. It has been known that curves of granularity number vs. screen resolution (lines per inch, “lpi”) are different with different toner particle sizes and with a uniform nominal toner particle size and different toner particle size distributions.
Noise reduction can be applied uniformly to all images, but this approach is inefficient, since some of the images may not benefit from noise reduction. In addition to allowing greater efficiency, variable noise reduction can produce better results. The application of a noise filter on an image often has an unintended consequence of reducing desirable image detail. Methods for designing and using Sigma filters are disclosed in U.S. Pat. No. 6,907,144 that attempt to minimize the loss of image detail while reducing the random noise present in a digital image. U.S. Pat. No. 5,923,775 to Snyder et al. discloses varying noise reduction based on characteristics of an image. U.S. Pat. No. 6,934,421 to Gindele et al. discloses varying noise reduction in accordance with the characteristics of a particular input source. U.S. Pat. No. 6,931,160 teaches use of a noise table in noise reduction. U.S. Pat. No. 7,065,255 to Chen et al. discloses method and apparatus, in which noise in digital images is reduced using a noise table that is selected based on metadata associated with the respective images.
It would thus be desirable to provide methods and systems, in which variable noise reduction is applied to electrostatographic printing of images.